This article provides information on the development of an adjustable spot welder implemented on the basis of the capacitor principle without a transformer. Also the scientific work considers the calculation of the energy of the capacitors for a spot welding apparatus using modern methods of numerical simulation and programming. The method of calculation is given, as well as a mathematical solution tool. The calculation results are compared with the experiment. Based on the data obtained, according to the results of calculations, work was carried out on a prototype, the result of which was an adjustable spot welder. It allows you to accurately and quickly weld nickel plates to lithium cells, creating full-fledged batteries from them, which are widely used in modern technology, including promising vehicles. The presence of sensors and a screen allows the operator to control the charging process and the direct operation of the unit, which simplifies the use of the device.